A new superfamily of DNA polymerases lacking homology with known polymerases has recently been discovered. They are error prone and have variable specificity for non-canonical substrates such as lesion- containing DNA. The first to be discovered in E. coli where REV1 in 1996 and the SOS-induced Po1 V in 1998, but others have been discovered throughout phylogeny and their functions remain unknown. Because the kinetic mechanisms of these new polymerases are likely to be different from those of known replicative polymerases, they provide an interesting area for biochemical study. This proposal will examine the kinetic mechanism of Pol IV, using quenched flow and stopped flow fluorescent pre-steady state methods. The mechanisms for normal polymerization as well as for lesion bypass and frameshift events will be analyzed. This will shed light on the function of Po1 IV in E. coli and provide insight into the mechanisms and functions of the other, newly discovered DNA polymerases.